This metal thing on the left is for the exhaust. Replace it along with the rubber seals on its top and bottom. One you’re certain everything is completed then put a thin bead of sealant around the main mating surfaces and put the bottom end back on the engine. You may need the help of a friend to get it in place and bolt it up. Be sure to use grease on all bolts. Be sure the copper water pipe is in place too.